The present invention relates broadly to a tracker apparatus, and in particular to a synthetic aperture multi-telescope tracker apparatus.
In the prior art, the use of multiple telescopes in a synthetic array has encountered a number of operational problems. One of these problems has been experimentally observed to involve low frequency drift in the optical far field pattern of the multiple telescopes. In order to keep the telescopes properly phased with respect to each other, it was required that manual compensation be provided. Furthermore, this manual compensation had to be performed on a continuous basis, since the various environmental disturbances that are encountered, will change the characteristics of the optical elements in the telescope system The telescope tracker apparatus provides an automated method by which this compensation can be performed. Another prior art problem that is encountered is the synchronization of the multiple telescopes in order that they operate in a manner similar to or resembling a single telescope. In addition, there arises numerous problems with respect to the correlation and processing of the telescope data. The use of multiple telescope arrays is further compounded by the utilization of telescope control and alignment systems which involve mechanical components such as high bandwidth piston loops. The Air Force Weapons Laboratory is currently conducting an in-house experiment to study the feasibility and complexities of phasing multple telescope arrays. In order to achieve true phasing between telescopes, the output from each telescope must be coherently summed at the same spot or reference point in the optical far field. The tilt and piston induced errors are the dominant barriers to effective phasing and must be corrected. In addition, the operation of control loops without some tracking of the low frequency errors tend to exhibit pronounced drift and the periodic loss of phasing over extended periods of time. The present invention is a multi-telescope tracker apparatus that utilizes a single set of electronics and a single photo-detection unit to simultaneously measure and compensate for errors in the operation of a multiple set of telescopes. A complementary filter pair within the tracker electronics allows the low frequency tracking error signals to be incorporated into the existing control loops with no significant loss of bandwidth and with improved temporal stability.